1. Field of the Invention
The present invention relates to an electron device in which plural thin film transistors each using an oxide semiconductor (particularly, a metal oxide semiconductor) are provided, and a method of manufacturing the relevant electron device. The electron device like this is generally used for a display device such as an electroluminescent (EL) device or a liquid crystal cell.
2. Description of the Related Art
In recent years, as described in Japanese Patent Application Laid-Open No. 2002-076356, a thin film transistor (TFT) in which a transparent conductive metal oxide polycrystalline thin film using ZnO as its main component is used as the channel layer has been actively developed.
Since the transparent conductive metal oxide polycrystalline thin film can be deposited at low temperature and is transparent in relation to visible light, it is possible by using the relevant film to form a flexible transparent TFT on a substrate such as a plastic sheet, a plastic film or the like.
Further, International Publication Pamphlet of WO 2005/088726 and “Nature”, Vol. 432 (2004-11), K. Nomura et al., pp. 488-492 describe a technique for using as the channel layer of an TFT a transparent amorphous metal oxide semiconductor film (a-IGZO) constituted by Indium, Gallium, Zinc and Oxygen. Further, these documents describe that a flexible transparent TFT having excellent field effect mobility of 6-9 cm2V−1 s−1 can be formed on a substrate such as a polyethylene terephthalate (PET) film or the like at room temperature.
Furthermore, “NIKKEI MICRODEVICES”, February 2006, p. 73 (FIG. 7) describes that SiON is used for an insulation layer and a device separation region of a thin film transistor which uses a-IGZO as the channel layer.
Generally, a TFT, including an amorphous silicon thin film transistor (TFT), is formed by a large number of micro fabrication processes. Therefore, in case of manufacturing the TFT which stably operates at low cost, it is important to simplify the micro fabrication process.
If the transparent semiconductor film consisting of Zn and O as described in Japanese Patent Application Laid-Open No. 2002-076356, International Publication WO 2005/088726 and “Nature” is used as the channel region of the TFT, the following problems occur. That is, a conductive transparent metal oxide channel region is formed by a photolithography method and dry etching or wet etching. Since the dry etching is generally performed by using an expensive vacuum system, it increases manufacturing cost. For this reason, it is effective to use the wet etching in order to reduce the manufacturing cost. However, in the wet etching, there is a case where throughput decreases due to deterioration of accuracy in the micro fabrication process, limitation of device size by absorbed moisture to the channel region by a wet process, addition of a dry process, and the like.